1. Field of the Invention
The present invention relates to a slider for a zip fastener and, more particularly, to a zip slider incorporating a mechanism to retain a pull tab in a closed position which then prevents vibration of the pull tab relative to the slider body.
2. Description of Related Art
Anti-vibration zip sliders are known per se. Typically, such a slider will have a body comprising upper and lower interconnected elements which cooperate to provide the entry channels via which, during relative motion of the zip tape and slider, the zip teeth are fed into or out of a single, central channel where the zip teeth knit or unknit during fastening or unfastening of the zip. Typically, the slider will additionally comprise a spring-loaded locking prong mounted on the slider body, which projects into the central channel. The locking prong is typically formed from a leaf spring material and, in use, bears against the knitted zip teeth thereby to prevent unwanted movement of the slider. A pull tab, pivotally mounted on the body is the means by which a user moves the slider. The pull tab has a cam formed at pivoting axis which, typically, cooperates with a follower surface provided on the same leaf spring element from which the locking prong is formed. When the pull tab 60 lies flat against the upper element of the slider body in a ‘closed’ or ‘resting’ position, the follower surface of the leaf spring acts on the cam to provide a resting bias and to bias the pull tab 60 into the resting position; and the locking prong—formed at the other end of the same leaf spring element—is allowed project fully into the channel and to bear against the zip teeth to lock the position of the zip slider. Conversely, when the pull tab is pivoted out of the resting position, to a position in which it is pivoted away from the body to enable a user to hold it, the cam acts on the follower surface of the leaf spring element to cause the locking prong to lift from the zip teeth, thereby unlocking the zip slider and enabling relative motion of the slider and teeth. In this way, a zip slider can be provided which has locking capability and, at the same time, when locked, whose pull tab is retained in a closed position without the possibility of vibration against the slider body.
Most usually, when the zip slider is in the locked position the locking prong will bear on the zip teeth in a ridge created between two adjacent teeth. In such a position, the locking prong will adopt its position of greatest displacement into the channel. That, in turn, means that the force applied on the cam of the pull tab by the follower surface to bias the pull tab into the resting position will then be at its greatest. Occasionally, however, the relative displacement of the zip slider and zip teeth is such that the locking prong will bear upon the top of a single zip tooth. The consequence of this is that the follower surface then bears less strongly against the cam and so applies a lesser biasing force with the result that the pull tab may then either move a little from the resting position or move a little more easily from that position. Either outcome can give rise to vibration and possibly noise. This is undesirable.